Modern communications and computer technologies greatly stimulate development of compact devices and systems. In particular, it can be related to filters, managing frequency responses, which are indispensable components in electronic systems including wire and wireless devices. Artificially-created periodicity in arrangement of same elements is one of the most fundamental approaches to design new materials and new types of microwave and optical components.
In particular, such approach is realized in forming an Electromagnetic Band Gap (EBG) structure (known also as Photonic Band Gap (PBG) structures, or Photonic Crystals, or Electromagnetic Crystals). In particular, these structures demonstrate an extremely-high attraction as filters because a band gap can be used to stop effectively signal transmission and a region out of the band gap can be applied for the pass of signals. Also, a defect in the EBG structure can lead to filters showing high Q (quality-factor) pass characteristics within the band gap.
Printed board technologies are widely applied as a cost-effective approach to develop different types of electronic equipment. Various planar transmission line structures based on these technologies are applied to obtain band gap effect and, as results, to develop different types of filtering components. However, the EBG structure can be considerably extended in dimensions, because a number of periodic cells to achieve a high-quality EBG effect can be large enough. This is a significant limitation of application of the EBG structure in actual devices, especially, at microwaves.
The application of the EBG concept to design compact components including filters is strongly limited, especially at microwave, because a band gap effect occurs due to periodical perturbations in a transmission medium. In this case, a lattice constant of such medium can be approximately equal to a half of the wavelength in the medium. As a result, dimensions of the structure providing the band gap effect in a planar periodical transmission line formed in a substrate can be considerably larger than the operating wavelength and cannot be acceptable for an electronic device. Also, the EBG structure based on a defected ground surface in a substrate can lead to a considerable increase of radiation (leakage losses) from the structures that can excite EMI problems in a designing device.
In conjunction with the above description, an antenna apparatus is disclosed in Japanese Laid Open Patent application (JP-P2003-304113A). In this conventional example, a monopole antenna excited through a coaxial line is provided at a center portion of a metal plate, on whose surface, a dielectric plate is formed. Thereby, the monopole antenna resonates at a specific frequency to the plate as a first substrate. Small regular hexagonal shaped metal plates are arranged in a 2-dimensional array in a constant interval on the surface of the dielectric plate in an external circumferential portion. A contact is formed to connect between the small metal plate and the metal plate, and an HIP substrate is formed as a second substrate which has a band gap to prevent propagation of electromagnetic wave of the above-mentioned specific frequency. Thus, the radiation of the electromagnetic wave of the specific frequency excited by the monopole antenna from a back side is restrained by the second substrate. In this way, the radiation from the back surface of the plate board is suppressed and enough antenna gain can be obtained to attain the resonance of the antenna.
Also, a connection structure of a strip line is disclosed in Japanese Laid Open Patent application (JP-P2006-246189A). In this conventional example, the connection structure of the strip line connects a first strip line and a second strip line, which are formed in different layers of a dielectric substrate, in a laminate direction through a connection section. A first removal section is formed where a grounded conductor pattern is removed, such that a strip conductor pattern connecting conductor constituting the connection section by connecting a tip portion of the strip conductor pattern of the first strip line and a tip portion of the strip conductor pattern of the second strip line, can penetrate without electrical contact with the grounded conductor pattern which is provided for the dielectric substrate between the first strip line and the second strip line. Second removal sections where the grounded conductor pattern is removed are provided periodically or approximately periodically for the grounded conductor of the first strip line and the grounded conductor of the second strip line.
Also, EBG material is disclosed in Japanese Laid Open Patent Application (JP-P2006-253929A). In this conventional example, a plurality of inductance elements are formed on the front surface of a first substrate. A second substrate has a dielectric substance provided on a rear surface side of the first substrate, and a conductor plate arranged on the opposite side to the first substrate with respect to the dielectric substance. A plurality of small metal plates are arranged above the plurality of inductance elements to be equally distanced to each other. The plurality of small metal plates are connected with the plurality of inductance elements by a plurality of connecting sections, respectively.